CN111382550B - Dynamic combination real-time simulation method of modular multilevel converter and use method - Google Patents
Dynamic combination real-time simulation method of modular multilevel converter and use method Download PDFInfo
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Abstract
The invention discloses a dynamic combination real-time simulation method and a use method of a modular multilevel converter, wherein the simulation method comprises the following steps: sequentially using a bridge arm average value model and a bridge arm equivalent circuit model for the MMC within a single step length of real-time simulation; the bridge arm average value model is executed in the electric element calculation stage, and a bridge arm equivalent voltage source is calculated; and calculating the capacitance voltage and the sum of the capacitance voltage of the submodule of each bridge arm of the MMC by using the bridge arm equivalent circuit model, and calculating the bridge arm average value model in the next simulation step length, wherein the calculation and the circuit matrix calculation are completed in parallel. The using method comprises the following steps: in a system containing a plurality of MMCs, part of the MMCs adopt a bridge arm equivalent circuit model, and the rest of the MMCs adopt the dynamic combination real-time simulation method and multiplex an improved bridge arm equivalent circuit model calculation module. The invention can reduce the computing resource requirement and hardware cost of the real-time simulator on the premise of ensuring the valve level control verification function, computing real-time performance and accuracy of all the sub-modules of the MMC.
Description
Technical Field
The invention relates to the technical field of electromagnetic transient real-time simulation of a power system, in particular to a dynamic combination real-time simulation method and a using method of a modular multilevel converter.
Background
The flexible direct-current transmission system based on the Modular Multi-Level Converter (MMC) solves the problems of high harmonic content, high switching frequency and the like of a two-Level Converter and a three-Level Converter, and is applied to a plurality of high-voltage direct-current projects at home and abroad. Research and engineering application of the flexible direct-current transmission system are also developed from a double-end system to a complex multi-end direct-current network, and the circuit topology and the complexity of a control and protection system of the flexible direct-current transmission system also bring challenges to safe and stable operation of an alternating-current and direct-current power grid.
The electromagnetic transient simulation is used for solving a system circuit in a time domain, and is commonly used for the research of an electromagnetic transient phenomenon of a power system, the research of a control protection algorithm and the like. The real-time simulation requires that the circuit calculation time is completed within the actual corresponding physical time, and the hardware-in-loop test of the power system device and the control protection device can be realized. The real-time simulation has wide application in the aspects of research, design, test, personnel training and the like of the power system, and is also an important tool for carrying out research and test on the MMC and the AC/DC network.
Fig. 1 is a schematic diagram of a conventional modular multilevel converter and half-bridge sub-module topology. An MMC consists of 6 legs, each leg containing n half-bridge Sub-modules (SM), where n can be as high as several hundred in a hvdc transmission system. The inside of the dotted line frame at the upper right corner of fig. 1 is the topological structure of each half bridge sub-module, which is composed of two Insulated Gate Bipolar Transistors (IGBTs) (T) 1 And T 2 ) And a diode (D) connected in anti-parallel with each transistor 1 And D 2 ) IGBT module and that constituteA capacitor C. When the traditional discrete component modeling is adopted, thousands of electrical nodes exist in a system matrix, and the existing computing equipment cannot realize real-time computation under the scale circuit. Researchers have therefore proposed a number of simplified algorithms to reduce electrical nodes. Document 1 (u.n.gn. Ananarthna, a.m.gold and r.p.jayasinghe, "Efficient Modeling of Modular Multilevel HVDC Converters (MMC) on Electromagnetic transfer protocols," in IEEE Transactions on Power Delivery, vol.26, no.1, pp.316-324, jan.2011.) models IGBT modules with two different resistances, simplifies half-bridge sub-modules by a davinan equivalent method, and can realize a large reduction in electrical nodes by adding equivalent voltages and resistances connected in series in the same bridge arm. Document 2 (T.Maguire, B.Warkentin, Y.Chen, and J.Hasler, "effective technologies for Real Time Simulation of MMC Systems," Proceedings of the International Conference on Power Systems in variables, canada, jul.18-20, 2013.) and document 3 (W.Li and J.B. Langer, "An effective Circuit for modeling and Simulation of modulated Multilevel Converters in Time HIL Test Bench," in IEEE Transmission on Power Simulation, 31, 2405, 2401-pp 9, otct.2016) respectively set forth a substitution Circuit and a further substitution Circuit, which respectively set forth An ideal Circuit for half bridge Circuit Simulation, which respectively set forth An ideal Circuit for calculating the Equivalent voltage of the IGBT submodule, which is simply a half bridge module, and which set forth a further calculation of the Equivalent voltage of the IGBT submodule 1 When the half-bridge submodule is switched on, the capacitor voltage of the half-bridge submodule is switched on, and when T is 2 The half-bridge sub-module bypasses at turn-on.
The bridge arm average model proposed by literature 4 (J.Peralta, H.Saad, S.Dennitiere, J.Mahseredjian and S.Nguefeu, "stepped and Averaged Models for a 401-Level MMC-HVDC System," in IEEE Transactions on Power Delivery, vol.27, no.3, pp.1501-1508, july 2012 ") is also commonly used for MMC modeling, and has fast calculation speed and higher accuracy in System transient research. Unlike the simplified model mentioned above, the mean value model ignores the valve level control of the sub-modules and assumes that the capacitor voltages of the sub-modules are fully balanced and therefore cannot be used for verification and testing of the valve level control and capacitor voltage balancing algorithms.
The calculation of the electromagnetic transient real-time simulation under each step length mainly comprises an electric element calculation part and a system matrix calculation part, and the two parts need to be executed in sequence. Because the equivalent circuit model of each MMC needs to calculate the capacitance of thousands of sub-modules and sum the equivalent voltage sources of the sub-modules on each bridge arm, the amount of calculation is large, and in order to realize real-time simulation calculation, a Field Programmable Gate Array (FPGA) is usually adopted as a calculation platform by a simulator. Two or more MMCs exist in the flexible direct current power transmission system, and in order to guarantee the real-time performance of calculation, more FPGA chips or board cards are needed to be used, or FPGA models with more logic resources are needed to be used, so that the hardware cost of the simulator is high in the application of real-time simulation of the flexible direct current power transmission system.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides a dynamic combination real-time simulation method of a modular multilevel converter. The invention aims to improve the utilization efficiency of computing resources during real-time simulation of a circuit containing a multi-MMC system and reduce the hardware cost of a simulator.
In order to achieve the purpose, the invention adopts the following technical scheme:
the invention provides a dynamic combination real-time simulation method of a modular multilevel converter, which is characterized in that a bridge arm average value model and a bridge arm equivalent circuit model are sequentially used for the modular multilevel converter within a single step length of real-time simulation; the bridge arm average value model is used for calculating an equivalent voltage source of each bridge arm in the modular multilevel converter, and the calculation of the model occurs in a real-time simulation electric element calculation stage; the bridge arm equivalent circuit model is used for calculating the capacitance voltage and the sum of all sub-modules in the bridge arm of the modular multilevel converter, the capacitance voltage sum of each sub-module in the bridge arm is used for calculating the bridge arm average value model in the next simulation step length, and the calculation of the model is performed in the circuit matrix calculation stage of real-time simulation and is completed in parallel with the circuit matrix calculation.
Further, the bridge arm equivalent circuit for which the bridge arm equivalent circuit model is used comprises any one of the following forms: the controllable voltage source model, the controllable voltage source and the fixed value resistor are connected in series, the controllable voltage source is connected in series with the variable resistor, the controllable current source is connected with the fixed value resistor in parallel, and the controllable current source is connected with the variable resistor in parallel.
Further, the sub-module structure in the modular multilevel converter comprises any one or more of a half-bridge sub-module, a full-bridge sub-module and a clamping sub-module.
The invention also provides a using method of the dynamic combination real-time simulation method, which is characterized in that in a system containing a plurality of modular multilevel converters, one or more modular multilevel converters adopt a bridge arm equivalent circuit model, and the rest modular multilevel converters adopt the dynamic combination real-time simulation method; the two parts of the modular multilevel converters are respectively multiplexed with a bridge arm equivalent circuit model calculation module based on the same calculation hardware in the electric element calculation stage and the circuit matrix calculation stage.
The characteristics and beneficial effects of the invention
The invention aims to improve the utilization efficiency of computing resources during real-time simulation of a circuit containing a multi-MMC system and reduce the hardware cost of a simulator.
The invention provides a dynamic combination simulation method of a modular multilevel converter for electromagnetic transient real-time simulation. The dynamic combination real-time simulation method provided by the invention has the valve level control verification function on all MMC sub-modules in a system circuit, improves the use efficiency of an FPGA calculation module in a simulator on the premise of ensuring the accuracy and the real-time performance of a simulation result, reduces the requirements on the number of FPGA board cards and the number of logic resources, and reduces the calculation hardware cost of the simulator.
The dynamic combination real-time simulation method provided by the invention comprises two parts when calculating the MMC, wherein an average value model is used for calculating equivalent voltage sources of a bridge arm in an electric element calculation stage, the calculation number of the capacitance voltage of each MMC is reduced to 6 from 6n required by the equivalent circuit model of the bridge arm, an equivalent circuit method is used for calculating the capacitance voltage of 6n half-bridge sub-modules of the MMC in a system circuit matrix calculation stage, and the correction calculation is carried out on the sum of the equivalent capacitance voltage required by the average value model in the next long calculation.
In the real-time simulation of a circuit comprising a plurality of MMC systems, one or a part of MMC systems adopts a bridge arm equivalent circuit model for calculation, the calculation is realized in a bridge arm equivalent circuit model calculation module based on FPGA, the other MMC systems adopt a dynamic combination model, and the bridge arm equivalent circuit model calculation module based on FPGA is reused in a system circuit matrix calculation stage, so that the aim of reducing the calculation hardware cost of a simulator is fulfilled.
The calculation formula and the implementation mode of the dynamic combination real-time simulation method of the modular multilevel converter are explained in detail in the following detailed description, and the content of the invention can be more clearly understood by referring to the description of the attached drawings.
Drawings
The foregoing and/or additional aspects and advantages of the present invention will become apparent and readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:
FIG. 1 is a schematic diagram of a prior art modular multilevel converter and half-bridge sub-module topology;
fig. 2 is a flowchart of a dynamic combination real-time simulation method of a modular multilevel converter according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of a method for calculating an average value model of a bridge arm of a modular multilevel converter in the related art;
FIG. 4 is a schematic diagram of a related art modular multilevel converter bridge arm equivalent circuit model calculation method;
fig. 5 is a schematic diagram of an application example of a dynamic combination real-time simulation method of a modular multilevel converter according to an embodiment of the present invention.
Detailed Description
Reference will now be made in detail to the embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar variables and elements or variables and elements having the same or similar functions throughout. The embodiments described below with reference to the drawings are illustrative and intended to be illustrative of the invention and are not to be construed as limiting the invention.
The dynamic combination real-time simulation method and the use method of the modular multilevel converter provided by the embodiment of the invention are described below with reference to the attached drawings.
The invention provides a dynamic combination real-time simulation method of a modular multilevel converter, which sequentially uses a bridge arm average value model and a bridge arm equivalent circuit model for the modular multilevel converter within a single step length of real-time simulation; the bridge arm average value model is used for calculating an equivalent voltage source of each bridge arm in the modular multilevel converter, and the calculation of the model occurs in a real-time simulation electric element calculation stage; the bridge arm equivalent circuit model is used for calculating the capacitance voltage and the sum of all sub-modules in a bridge arm of the modular multilevel converter, the capacitance voltage value of each sub-module is used for inputting an MMC control algorithm, the capacitance voltage sum of each sub-module in the bridge arm is used for calculating a bridge arm average value model in the next simulation step length, and the calculation of the model is performed in a circuit matrix calculation stage of real-time simulation and is completed in parallel with the circuit matrix calculation.
Fig. 2 is a calculation flowchart of a dynamic combination real-time simulation method of a modular multilevel converter according to an embodiment of the present invention. The simulated modular multilevel converter and the half-bridge sub-module topological structure thereof are shown in figure 1, wherein the MMC is composed of 6 bridge arms, each bridge arm comprises n half-bridge sub-modules SM, the structures of the half-bridge sub-modules are the same, and the half-bridge sub-modules respectively comprise two IGBTs (T) 1 And T 2 ) And diodes (D) connected in anti-parallel with the IGBTs 1 And D 2 ) The IGBT module and a capacitor C.
The dynamic combination simulation method of the invention respectively comprises two stages of an electric element calculation stage and a circuit matrix calculation stage under each step length delta T (comprising five calculation steps S1 to S5, wherein the steps S1 to S3 are completed in the electric element calculation stage, and the steps S4 to S5 are completed in the circuit matrix calculation stage), and specifically comprises the following steps:
i, calculation stage of electric element
Step S1, calculating a bridge arm equivalent capacitance switching function S by using an MMC average value model shown in figure 3 ave (t), the concrete method is as follows：
At the starting time t of the current step length, setting the capacitance voltage balance of all half-bridge sub-modules, and equating the capacitances of n half-bridge sub-modules to a switched function s ave (t) a controlled equivalent capacitance, the switching function s ave (T) passing T in each half-bridge submodule 1 Of the grid signal
And calculating according to the following formula:
in the formula, the upper corner mark i represents the serial number of the half-bridge sub-module, and the lower corner mark 1 represents the T in the half-bridge sub-module 1 The same applies below.
Two IGBTs (T) in the half-bridge sub-module during normal operation 1 And T 2 ) Can not be conducted at the same time, and can be judged by the current direction when being locked
Equivalent on-off states.
Step S2, respectively calculating equivalent capacitance voltages of 6 bridge arms in the MMC through a bridge arm average value model (equivalent capacitances of the 6 bridge arms are equal), wherein the calculation formula is as follows:
i Ceq (t-ΔT)＝s ave (t-ΔT)i arm (t-ΔT) (2)
wherein,
in the formula, C sm The capacity value of the half-bridge submodule is (the capacity value of each half-bridge submodule is equal); i.e. i arm (T- Δ T) is the bridge arm current at the last moment; c eq Is a bridge arm equivalent capacitance; i.e. i Ceq (T- Δ T) is the current passing through the equivalent capacitance of the bridge arm calculated according to the bridge arm current at the last moment; v. of Ceq And (t) is the voltage at two ends of the equivalent capacitor of the bridge arm at the current moment. Due to the current i at two ends of the equivalent capacitor of the bridge arm Ceq Under the influence of a switching function, in order to avoid introducing a variable resistor into the equivalent model of the bridge arm, a foremate Euler method is adopted to calculate the voltage v at two ends of the equivalent capacitor of the bridge arm Ceq 。
S3, respectively calculating the equivalent voltage source voltage v of 6 bridge arms in the MMC arm (t)(v arm (t) is an equivalent voltage source of any one bridge arm in the MMC, and the calculation methods of 6 bridge arms are the same), the formula is as follows:
v arm (t)＝s ave (t)v Ceq (t), (5)
and the equivalent voltage source voltage of the bridge arm is used as a main variable in a system circuit model, and the current vector in the system matrix is changed at each calculation step length.
II, circuit matrix calculation stage
Simultaneously with the system matrix calculation, the dynamic combination model completes the calculations of step 4 and step 5 (corresponding to equations (6) - (11)). Fig. 4 is a schematic diagram of a modular multilevel converter bridge arm equivalent circuit model calculation method.
In step S4, calculating the capacitance voltage of all half-bridge sub-modules of the MMC through a bridge arm equivalent circuit model
The method is used for MMC controller input, and the specific calculation formula is as follows:
in the formula, R cap For the equivalent impedance of the half-bridge sub-module capacitors (the same impedance value for each half-bridge sub-module),
and &>
And respectively calculating the current and the historical voltage source of each half-bridge submodule capacitor under the last step length, wherein the upper corner mark i is the serial number of each half-bridge submodule. As shown by the dashed box in fig. 4, the IGBT module may be equivalent to a variable resistor r 1 And a variable resistor r 2 The IGBT is subjected to idealized processing in a bridge arm equivalent circuit model, and the resistance of the device is considered to be infinite when the device is turned off and 0 when the device is turned on. When T is 1 Of the gate signal s 1 Is 1,T 2 Of the grid signal s 2 When it is 0, the variable resistance r 1 Is 0, variable resistance r 2 Is infinite, and is equivalent to a capacitor connected into a bridge arm circuit at the moment, and the current of the capacitor of the half-bridge submodule is greater than or equal to the maximum value>
Equal to bridge arm current i arm (T- Δ T); when T is 1 Of the gate signal s 1 Is 0,T 2 Of the gate signal s 2 When 1, the variable resistance r 1 Is infinite, variable resistance r 2 Is 0, which is equivalent to a capacitor bypass, the current of the half-bridge sub-module capacitor &>
Equal to 0. (in the equivalent circuit model calculation process shown in FIG. 4, the half-bridge submodule equivalent voltage source voltage is further solved for->
And for all half-bridge sub-module voltage source voltages ≥ for a single bridge arm>
Summing to calculate bridge arm equivalent voltage source voltage v arm (t) of (d). V in dynamic combinatorial real-time simulation method arm (t) has been solved in step S3, so the method does not use the bridge arm equivalent circuit model to calculate v arm (t), step S5 is performed. )
S5, calculating the sum v of the capacitance and the voltage of the half-bridge submodule in each bridge arm of the MMC Ctot (t) as v required for step S1 in the next simulation step Ceq (t), the specific formula is as follows:
v Ceq (t)＝v Ctot (t) (11)
and (3) finishing the calculation of the dynamic combination simulation method of the modular multilevel converter in the current simulation step length delta T, enabling T = T + delta T when the next simulation step length is started, returning to the step S1, and repeating the steps in a circulating manner until the preset simulation end time is reached.
It should be noted that the calculation of step S4 and step S5 is related to the number n of half-bridge submodules in the bridge arm, and when n is several hundred, the calculation amount of step S4 and step S5 is much larger than that of steps S1 to S3.
Fig. 5 is a schematic diagram of an application example of the dynamic combination real-time simulation method for the modular multilevel converter according to the present invention. In multi-MMC system circuit real-time simulation, where k 1 The MMCs are calculated using An existing bridge arm Equivalent Circuit model (e.g., using the bridge arm Equivalent Circuit model described in document 3, document 3 2 The MMC uses the dynamic combination simulation provided by the inventionA method is provided. In addition, other circuit element calculations, such as three-phase power supplies, transformers, transmission lines and the like, and calculations of basic control elements are also included in the real-time simulation implementation. When the electric element is calculated, a current source vector I in the circuit matrix and an inverse matrix G of the circuit admittance matrix are generated -1 And multiplying the current source vector I to obtain a node voltage vector V. When V is known, i required by the next step length can be obtained by solving bridge arm inductive current arm (t-ΔT)。
k 1 The MMC is designed based on the FPGA for a bridge arm equivalent circuit calculation module and carries out model calculation in the electric element calculation stage to obtain the voltage v of all bridge arm equivalent voltage sources arm (t) for subsequent circuit matrix calculations. k is a radical of formula 2 When the MMC is calculated by adopting the dynamic combination simulation method provided by the invention, firstly, a bridge arm average value calculation module designed based on a CPU or FPGA is used for carrying out model calculation (namely, the steps S1 to S3 are executed) in the electric element calculation stage to obtain the voltage v of all bridge arm equivalent voltage sources arm (t) for subsequent circuit matrix calculations; gate signal of each IGBT and each bridge arm current i arm (t) is used to complete steps S4 and S5 in the circuit matrix calculation stage. In order to complete the steps S4 and S5, k is multiplexed without designing a calculation module separately 1 And the bridge arm equivalent circuit calculation module based on the FPGA is used by the MMC. Since step S4 and step S5 are completed in the circuit matrix calculation stage, k is not equivalent to k using the traditional bridge arm equivalent model 1 The calculation of the MMC generates time sequence conflict, so the dynamic combination model in the invention can reduce the use of FPGA calculation resources on the premise of ensuring the real-time and accuracy of the calculation.
Step S4 in the dynamic combination model is the same as the method for calculating the capacitance voltage of the half-bridge sub-module in the conventional bridge arm equivalent circuit model, but step S5 is different from the conventional bridge arm equivalent circuit model, and the following method can realize the multiplexing of the calculation modules:
when entering the traditional equivalent circuit model calculation mode:
in the formula v sm For submodule equivalent voltage source, from s 1 And s 2 And determining whether the capacitor voltage is switched on. When entering the step S5 of the dynamic combination method, order
Is->
The calculated output value is the sum of the capacitor voltages, which is equivalent to equation (10) in step S5. By this modification, k in FIG. 5 1 MMC and k 2 The MMC respectively multiplexes a bridge arm equivalent circuit model calculation module based on the same calculation hardware in an electric element calculation stage and a circuit matrix calculation stage.
K in simulation implementation 1 And k is 2 Is compared with the time delta T allocated to the calculation of the electrical component in the simulation calculation 1 And calculating Δ T by assigning to the circuit matrix 2 The relationship, Δ T without increasing a single step, is as follows:
when the resource consumption of the average value calculation is neglected, the saved FPGA logic resource proportion eta is about:
it should be noted that when Δ T can be adjusted in a small range, the condition of formula (13) may not be satisfied when the dynamic combination model is used. Except for a calculation module in the MMC equivalent circuit, other electric or control element calculation, an MMC average value model and system matrix solving calculation can be finished in a CPU or a corresponding calculation module can be designed in an FPGA.
The formulas presented in this specification are exemplary. The formula introduced in the specification can clearly introduce a modeling method, and part of the formula can be simplified when the simulator is realized. The specification describes a calculation formula of an MMC half-bridge submodule, and the dynamic combination model is also suitable for an MMC topology with a full-bridge submodule, a clamping double submodule and a mixed submodule. When the method is used for the MMC with a full-bridge submodule, a clamping double submodule and a mixed submodule, the formula (1), the formula (4) and the formula (8) in the step S1 and the step S4 are modified according to the average value model of the corresponding submodule and the equivalent circuit model calculation method, and the calculation steps of the method are not changed by the modification. In this example, the equivalent element of the MMC bridge arm in the system circuit calculation uses a controllable voltage source, and the equivalent element may also adopt a form of a voltage source connected in series with a constant-value battery, a controllable voltage source connected in series with a variable resistor, a controllable current source connected in parallel with a constant-value resistor, a controllable current source connected in parallel with a variable resistor, or the like. When the equivalent element contains a fixed value or a variable impedance, the equivalent capacitance calculation in step S2 of the embodiment of the present invention does not use the forward-term euler method, but uses the backward-term euler method or the trapezoidal integration method, i.e., modifies the formula (3). The FPGA in the model implementation mode refers to an FPGA chip and also refers to FPGA logic resources in an on-chip integrated system.
The present invention and its embodiments have been described above schematically, without limitation, and what is shown in the drawings is only one of the embodiments of the present invention and is not actually limited thereto. Therefore, if the person skilled in the art receives the teaching, it is within the scope of the present invention to design the similar manner and embodiments without departing from the spirit of the invention.
Claims (3)
1. A dynamic combination real-time simulation method of a modular multilevel converter is characterized in that a bridge arm average value model and a bridge arm equivalent circuit model are sequentially used for the modular multilevel converter within a single step length of real-time simulation; the bridge arm average value model is used for calculating an equivalent voltage source of each bridge arm in the modular multilevel converter, and the calculation of the model occurs in a real-time simulation electric element calculation stage; the bridge arm equivalent circuit model is used for calculating the capacitance voltage and the sum of all sub-modules in the bridge arm of the modular multilevel converter, the capacitance voltage sum of each sub-module in the bridge arm is used for calculating the bridge arm average value model in the next simulation step length, and the calculation of the model occurs in the circuit matrix calculation stage of real-time simulation and is completed in parallel with the circuit matrix calculation;
the modularized multi-level converter is composed of 6 bridge arms, each bridge arm comprises n half-bridge sub-modules, the structures of the half-bridge sub-modules are the same, and each half-bridge sub-module respectively comprises an insulated gate bipolar transistor module consisting of two insulated gate bipolar transistors and diodes in inverse parallel connection with the insulated gate bipolar transistors, and a capacitor C; setting the calculation step length of the dynamic combination real-time simulation method as delta T, the method specifically comprises the following steps:
i, calculation stage of electric element
Step S1, calculating an equivalent capacitance switching function S of a bridge arm by using a bridge arm average value model ave (t)
At the starting time t of the current step length, setting the capacitance voltage balance of all half-bridge sub-modules, and equating the capacitances of n half-bridge sub-modules to a switched function s ave (t) a controlled equivalent capacitance, the switching function s ave (T) by means of an insulated gate bipolar transistor T in each half-bridge submodule 1 Of the grid signal
The formula is as follows:
in the formula, an upper corner mark i represents the serial number of a half-bridge submodule;
when the half-bridge submodule operates normally, two insulated gate bipolar transistors in the half-bridge submodule cannot be conducted simultaneously, and when the half-bridge submodule is locked, the current direction is used for judging
Equivalent on-off state;
s2, respectively calculating equivalent capacitance voltages of 6 bridge arms in the modular multilevel converter through the average value model of the bridge arms, wherein the formula is as follows:
i Ceq (t-ΔT)＝s ave (t-ΔT)i arm (t-ΔT) (2)
wherein,
in the formula, C sm Is the capacity value of the half-bridge submodule; i.e. i arm (T- Δ T) is the bridge arm current at the previous moment; c eq Is a bridge arm equivalent capacitor; i.e. i Ceq (T- Δ T) is the current passing through the equivalent capacitance of the bridge arm calculated according to the bridge arm current at the last moment; v. of Ceq (t) is the voltage at two ends of the equivalent capacitor of the bridge arm at the current moment;
s3, respectively calculating equivalent voltage source voltages v of 6 bridge arms in the modular multilevel converter arm (t), the formula is as follows:
v arm (t)＝s ave (t)v Ceq (t), (5)
II, circuit matrix calculation stage
S4, calculating the capacitance voltage of all half-bridge sub-modules in the modular multilevel converter through the bridge arm equivalent circuit model
The formula is as follows:
in the formula, R cap Equivalent impedance of each half bridge submodule capacitor is equal;
and/or>
Respectively calculating the current and the historical voltage source of each half bridge submodule capacitor at the last step length;
s5, calculating the sum v of the capacitance and the voltage of the half-bridge sub-modules in each bridge arm of the modular multilevel converter Ctot (t) as v required for step S1 in the next simulation step Ceq (t), the formula is as follows:
v Ceq (t)＝v Ctot (t) (11)
and when the calculation of the dynamic combination simulation method of the modular multilevel converter in the current simulation step length delta T is finished, when the next simulation step length is started, making T = T + delta T, returning to the step S1, and repeating the steps in a circulating manner until the preset simulation end time is reached.
2. The dynamic combinatorial real-time simulation method of claim 1, wherein the bridge arm equivalent circuit for which the bridge arm equivalent circuit model is used comprises any one of the following forms: the controllable voltage source model, the controllable voltage source and the fixed resistor are connected in series, the controllable voltage source and the variable resistor are connected in series, the controllable current source and the fixed resistor are connected in parallel, and the controllable current source and the variable resistor are connected in parallel.
3. The use method of the dynamic combination real-time simulation method according to claim 1 or 2, wherein in a system comprising a plurality of modular multilevel converters, one or more modular multilevel converters adopt a bridge arm equivalent circuit model, and the rest modular multilevel converters adopt the dynamic combination real-time simulation method; the two parts of modular multilevel converters multiplex a bridge arm equivalent circuit model calculation module based on the same calculation hardware respectively in an electric element calculation stage and a circuit matrix calculation stage.
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